With the rise of an intelligent terminal such as a smart phone, a tablet computer, and the like, all the past applications on the Internet will be reproduced on a mobile terminal. Current 2G/3G network has been unable to satisfy the requirement of mobile data service of a plenty of intelligent terminals. A rise of Long Term Evolution (Long Term Evolution, LTE) greatly broadens a bandwidth of the network, and a rate experience of 100 Mbps may be provided for a user in case of a 20 MHz of spectral bandwidth. However, a great challenge is still posed to the network for a densely populated area such as a shopping center, a station, an airport, a crowded section of a highway, and so on.
Wireless fidelity offload (Wi-Fi Offload, wireless fidelity Offload) which is currently a hot topic, is a good idea, whereby WiFi hot-spots are widely deployed in a densely populated area, and a Wi-Fi communication may be activated when a user needs a wideband data service. Wi-Fi, a wireless local network standard developed and maintained by a WiFi Alliance of IEEE, is a wireless communication technology with short distance, and is capable of supporting a radio electric signal accessed from the Internet within a range of hundreds of feet. The advantages of deploying the Wi-Fi lie in freedom, flexibility, and the use of free frequency spectrums without being charged, while with the disadvantage of difficult to be regulated by an operator.
Therefore, an urgent problem to be faced is to provide a network standard with wireless short-distance and hot-spot coverage that is capable of meeting the requirements of the operators. Currently, 3GPP gradually improves establishment of a standard for a pico cell (pico cell), a micro cell (micro cell) and the like. For network coverage, pico cell coverage will be added in a hot-spot area so as to achieve an offload of user data and to prevent a large number of users from performing data transmissions on a macro network at a same time. In such coverage scenario, behaviors of both an intelligent terminal and the network will be changed, and when an intelligent terminal moves into a pico cell, the intelligent terminal may select to reside in the pico cell or still reside in a macro cell while the service data being transmitted through the pico cell.
An indoor wireless hot-spot small cell (Small cell) coverage technology is a service offload access point similar to a pico cell. A small cell is mainly deployed under a macro cell to provide a broadband data offload service with low mobility on a hot-spot. In the case that a small cell whose control plane and user plane are separated is jointly deployed with a macro base station (eNodeB), a connection relationship between a user equipment (User Equipment, UE), the small cell and the eNodeB are as shown in FIG. 1. Link 1 is a connection between the UE and the eNodeB, and link 2 is a connection between the UE and the small cell. A control plane of the UE, that is, signaling radio bearers ((Signaling Radio Bearer, SRB) 0, SRB 1, and SRB 2), are established on the eNodeB, while a data radio bearer (Data Radio Bearer, DRB) is established on the small cell for service offload. The UE transmits control signaling through the eNodeB, and transmits service data through the small cell. In a current LTE network, after establishing a radio resource control (Radio Resource Control, RRC) connection with the eNodeB, the UE needs to detect in-sync/out-of-sync condition of a radio link continuously, and to report an in-sync/out-of-sync indication to an RRC layer. The RRC layer determines whether or not a radio link failure occurs. The RRC layer performs a radio link evaluation by employing a method in which a UE physical layer monitors signal quality of a customized ringing signal (Customized Ringing Signal, CRS), and detects signal condition of a downlink radio link of a serving cell. The UE evaluates downlink radio link quality, and compares the downlink radio link quality with a set threshold Qin/Qout. If the downlink radio link quality of the serving cell is worse than the Qout during an evaluation period, the physical layer reports an out-of-sync (Out-of-Sync) indication to the RRC layer. If the signal quality of the serving cell is higher than the Qin during the evaluation period, the physical layer reports an in-sync (In-sync) indication to the RRC layer. If the signal quality of the serving cell neither satisfies the condition for reporting the in-sync indication nor satisfies the condition for reporting the out-of-sync indication during the evaluation period, the physical layer would not report an indication to the RRC layer. A time interval between two consecutive reports of the in-sync/out-of-sync indications should be no less than 10 ms when the UE is in a non-discontinuous reception (Discontinuous Reception, DRX) state, and takes a maximum value of 10 ms and a DRX period when the UE is in a DRX state.
A process for recovering a radio link of the RRC layer provided by the prior art includes a first phase (First Phase) and a second phase (Second Phase), wherein the first phase is divided into the following two parts:
a phase for detecting a problem of the physical layer: if the RRC layer receives a number ‘N310’ of consecutive out-of-sync indications, then the RRC layer detects a problem in the UE's physical layer and starts T310, that is, a phase for recovering the problem of the physical layer starts; and
the phase for recovering the problem of the physical layer: if the RRC layer receives a number ‘N311’ of consecutive in-sync indications during a running period of the T310, the UE assumes that the problem in the physical layer has been recovered, and then stops the T310; and when the T310 expires, the UE starts T311, that is, a process for reestablishing the RRC connection starts.
When a failure of the radio link 1 in FIG. 1 occurs, the UE may attempt a process for recovering the radio link as shown in FIG. 2. If it is found that the failed radio link can not be recovered during the second phase of this process, the UE would go into an IDLE state according to a conventional mode, and stop current ongoing service transmission.
In one word, in the scenario that the small cell and the eNodeB are jointly deployed, a design idea of separating the control plane and the user plane enables effective reduce in occurrence probabilities of handing over, that is, after entering into a coverage area of the small cell, a UE just establishes a data bearer on the small cell without executing a handover command. Similarly, when the UE moves out of the coverage area of the small cell, it is also unnecessary to execute the handover operation. However, according to a conventional method for processing a radio link failure, if the radio link between the UE and the eNodeB is failed when the UE transmits data on the small cell, and the UE can not recover the radio link connection with the eNodeB, the UE needs to return to an RRC_IDLE state, while at this time, the data link between the UE and the small cell is normal and data transmission still can be performed. Therefore, the conventional method for processing the radio link failure is not suitable for the scenario that the control and the data are separated from each other under coordinated work of the macro cell and the pico cell.